A parallel hybrid drive vehicle which runs under the drive force of a motor or an engine, or both, is disclosed in pp. 39-52 of "Automobile Engineering", Vol. 46, No. 7 published in June, 1997 in Japan by Tetsudo Nihon Sha.
In this hybrid drive vehicle, when the load is small, the vehicle runs on the output of the motor alone, and when the load increases, the vehicle starts the engine to provide sufficient drive force.
On the other hand, during deceleration, so-called regenerative braking is performed wherein the motor is driven as a generator by the rotational energy of the drive wheels, and the power generated is used to charge a battery.